I can't get to the part where I upload my file.

Nobody has claimed this yet.

Clear output executed at 7:53 PM (0 minutes ago) executed in 13.212s

/usr/local/lib/python3.7/dist-packages/flax/optim/base.py:52: DeprecationWarning: Use `optax` instead of `flax.optim`. Refer to the update guide https://flax.readthedocs.io/en/latest/howtos/optax_update_guide.html for detailed instructions.
'for detailed instructions.', DeprecationWarning)
/usr/local/lib/python3.7/dist-packages/jax/_src/lib/xla_bridge.py:435: UserWarning: jax.host_count has been renamed to jax.process_count. This alias will eventually be removed; please update your code.
"jax.host_count has been renamed to jax.process_count. This alias "

Aditionally:

No files selected. Upload widget is only available when the cell has been executed in the current browser session. Please rerun this cell to enable.
---------------------------------------------------------------------------
MessageError Traceback (most recent call last)
in ()
4
5 log_event('uploadAudioStart', {})
----> 6 audio = upload_audio(sample_rate=SAMPLE_RATE)
7 log_event('uploadAudioComplete', {'value': round(len(audio) / SAMPLE_RATE)})
8

4 frames

/usr/local/lib/python3.7/dist-packages/google/colab/_message.py in read_reply_from_input(message_id, timeout_sec)
104 reply.get('colab_msg_id') == message_id):
105 if 'error' in reply:
--> 106 raise MessageError(reply['error'])
107 return reply.get('data', None)
108

MessageError: TypeError: google.colab._files is undefined
No idea what is going on.

Start by reproducing the notebook cell that calls upload_audio(sample_rate=SAMPLE_RATE) in Google Colab and inspect the reported google.colab._files error. Done means the upload widget becomes available and an audio file can be selected and loaded without the MessageError.

Written by the indexing model from the issue text.